The present invention relates to a system and method for communication between nodes of a closed loop local communication path.
Many efforts have been made to develop a ring type communications network because of the potential low cost and particularly because such a system can be implemented using fiber optic paths. Fiber optic data transmission is particularly attractive for a local communication system because of its immunity to electromagnetically induced noise.
The general objective of a ring distribution of processors is recognized, for example, in the text Computer Networks and Distributed Processing, by James Martin, Prentice-Hall, Inc., 1981, page 38, FIG. 3.2, the second illustration.
One of the traditional objections to such a ring type processing network relates to such a system wherein a central controller is required with a store and forward function with respect to each of the other nodes. In such a system, communication is dependent on the speed of operation of the central controller, and is less flexible because of the requirements that the central controller poll the recipient node prior to actual forwarding of the data. It would be desirable to avoid the use of a central controller not only for greater speed and flexibility of communication between the nodes of a closed loop communication path, but also to provide such a communication system where failure of a computer at one node would not prevent continued operation, as is the case where a central controller is present.
Other types of ring networks essentially involve a ring of data processing devices each of which must check an incoming message before forwarding it to the next node. In many check and forward systems communication is structured in relation to specified multiplex time slots or in relation to a circulating control message e.g. a so called token or "GO" control signal. In any event, complexity and added expense result from the necessity for recognizing the destination address of an incoming message within a processing cycle of brief time duration, and for selectively removing a message packet from the loop where the same originated at the local node and has traversed the loop. In one such proposed check and forward system, information was to be sent in individual packets eighteen bits in length including a total destination label size of eight bits, a data field of eight bits and start/stop bits.